This invention relates generally to nuclear reactors and more particularly, to assemblies for coupling core spray systems within such reactors.
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A shroud typically surrounds the core and is supported by a shroud support structure.
Boiling water reactors have numerous piping systems, and such piping systems are utilized, for example, to transport water throughout the RPV. For example, the reactor is configured for a core spray system to deliver cooling water to the reactor core during a loss of coolant accident. The core spray system, including piping, downcomers, T-box assemblies, and core spray spargers, is used to deliver water from outside the RPV to inside the RPV. The core spray system provides water to the reactor core.
Stress corrosion cracking (SCC) is a known phenomenon occurring in reactor components exposed to high temperature water, such as structural members, piping, fasteners, and welds. The reactor components are subject to a variety of stresses associated with, for example, differences in thermal expansion, the operating pressure needed for the containment of the reactor cooling water, and other sources such as residual stresses from welding, cold working and other inhomogeneous metal treatments. In addition, water chemistry, welding, heat treatment, and radiation can increase the susceptibility of metal in a component to SCC.
Reactor internal piping, such as core spray spargers and T-box assemblies, occasionally requires replacement as a result of SCC or for other reasons. Replacing the spray spargers sometimes requires removing and replacing T-box assemblies, and core spray piping, including downcomers. Replacement of spray spargers, T-boxes, and downcomers is complicated by the limited working space, high radiation levels, and difficulties associated with welding to a highly radioactive shroud.
In one aspect, a coupling apparatus is provided for a core spray system in a nuclear reactor pressure vessel. The coupling apparatus includes a shroud, a T-box housing, a downcomer elbow, a spider, and a draw bolt. The shroud includes an inner surface, an outer surface, and a shroud opening extending between the inner surface and the outer surface. The T-box housing includes an inlet, a first outlet, a second outlet, and a bolt opening opposed the inlet. The downcomer elbow includes a first end and a second end, the first end having an interior portion and an exterior portion. The spider is attached to the downcomer elbow first end interior portion. The draw bolt extends through the T-box housing bolt opening, the T-box housing inlet, and the shroud opening to engage the spider. The draw bolt couples the T-box housing inlet to the shroud inner surface. The draw bolt also couples the downcomer elbow to the shroud outer surface.
In another aspect, a coupling apparatus is provided for a core spray system in a nuclear reactor pressure vessel. The coupling apparatus includes a shroud, a T-box housing, a downcomer elbow, and a plurality of draw bolts. The shroud includes an inner surface, an outer surface, a shroud opening extending between the inner surface and the outer surface, and a plurality of bolt openings adjacent the shroud opening.
The T-box housing includes an inlet, a first outlet, a second outlet, a plurality of sidebrackets, and bolt openings in the sidebrackets. The downcomer elbow includes a mounting flange and a plurality of flange bolt receivers. The plurality of draw bolts extending through the T-box housing sidebrackets and the shroud bolt openings to engage the downcomer mounting flange bolt receivers, the draw bolts coupling the T-box housing inlet to the shroud inner surface and the downcomer elbow to the shroud outer surface.
In another aspect, a bracket assembly is provided for a core spray sparger in a nuclear reactor pressure vessel, the bracket assembly including a shroud, a core spray line, a fitted spacer, a draw bolt, a spherical washer, and a spherical nut. The shroud includes an inner face, an outer face, and a shroud bolt opening, the shroud bolt opening including a counterbore in the shroud inner face. The a core spray line includes a mounting bracket, the mounting bracket including a bolt receiver. The fitted spacer is sized to be received in the counterbore. The draw bolt includes an operating head, a bolt shaft extending from the operating head, a shaft periphery, and a plurality of scallops in the bolt shaft periphery. The bolt shaft includes a threaded section. The spherical washer includes a spherical cavity. The spherical nut includes a bolt keeper configured to be crimped to the shaft scallops, a spherical portion sized to be received in the spherical washer, the spherical nut maintaining compressive tension on the fitted spacer.
In another aspect, an end clamp assembly is provided for a core spray line. The core spray line includes an end cap and a plurality of spray nozzles in a nuclear reactor pressure vessel. The end clamp assembly includes an upper sleeve, a lower sleeve, a stop pin, and a plurality of clamp bolts. The upper sleeve includes an outer surface and at least one flange portion, each flange portion including a bolt opening. The lower sleeve is configured to couple to the upper sleeve and includes an outer surface, at least one bolt receiver, a stop pin opening and an end portion extending substantially perpendicularly from the lower sleeve. The stop pin extends through the lower sleeve stop pin opening into the core spray line. The clamp bolts extend through the upper sleeve flange portion to engage the lower sleeve bolt receiver, the lower sleeve end portion in contact with the sparger spray line end cap.
In another aspect, a core spray sparger in a nuclear reactor pressure vessel is provided. The core spray sparger includes a plurality of core spray lines, a coupling apparatus, a bracket assembly, and an end clamp assembly.